How do I test an LSTM-based reinforcement learning model using any Atari games in OpenAI gym?
If I understand your problem correctly, you can test on just about any environment, and just omit parts of the observations to ensure your RNN is learning. For example, you can test on cartpole, ignoring the velocity and angular velocity states. This way the MDP isn't actually Markovian and you'll need the RNN to learn.